1. Field of the Invention
This invention is directed to a camera that determines the stop value of a photographic lens based on the focal depth of the object or objects to be photographed.
2. Description of Related Art
When an object at a certain distance is brought into focus prior to being photographed, the resulting photograph is generally focused not only on that particular object, but also on objects in front of and behind the object. When the focus is adjusted to a certain position, there is a range of positions which are actually in focus. This range is called the photographic depth of field. It is known that the photographic depth of field increases as the diaphragm gets smaller. If the distance is fixed, the boundary depth grows larger as the focal length decreases. The term "diaphragm" refers to the F number that is widely used in photography-a larger F number means a diaphragm which is in a relatively more closed state, while a smaller F number means the diaphragm is in a relatively more open state. Furthermore, the photographic depth of field is smaller when the object in focus is at a close distance and is larger when the object is at a greater distance.
The focal depth is in front of and behind the focal surface of the photographic lens. The focal surface is the film surface on which the image of the object will be recorded. The focal depth describes the range in which picture portraits can be clearly photographed (not unfocused). The focal depth is larger on the photographic lens side of the focal surface and is smaller on the opposing (rear cover) side of the focal surface.
As a conventional method of performing photography under conditions in which multiple objects at differing positions, each with a different focus, are to be photographed, the photographer closes the diaphragm while peering through the finder and determines a stop value at which each object is in focus by confirming the state of each object (in other words, a stop value into which each object enters the photographic depth of field).
To obtain the objective stop value by this method, it is necessary for the photographer to be experienced. Amateurs are sometimes unable to perform acceptable photography using this method. In order to solve this type of problem, cameras have recently been introduced which are equipped with a photographic depth of field priority regulation device. Numerous cameras of this type are known, including, for example, the camera disclosed in Japanese unexamined patent application Sho 63-172129.
However, with cameras equipped with conventionally known photographic depth of field priority regulation devices, when multiple objects at differing positions are to be photographed, or when the stop value at which each object can be brought into focus is smaller than the smallest stop value of the lens installed on the camera, it becomes impossible for all of the multiple objects at the different positions to be brought into focus at the same time.
In this state, there are many cases in general in which a photograph that corresponds to the expectations of the photographer is produced by focusing on the object closest to the camera, but this type of correspondence is not made by the conventional camera described above, which causes an inconvenience to photographers.